Springboot三种启动方式

在https://start.spring.io/上创建一个springboot工程

生成的代码中的启动方式咱们暂时定义为默认方式：

/**
 * @auther: lawt
 * @date: 2018/12/1 17
 * @Description: 默认启动方式
 */
@SpringBootApplication
public class MicroServicesSpringBootApplication {
public static void main(String[] args) {
//端口默认为8080
        SpringApplication.run(MicroServicesSpringBootApplication.class, args);
    }
}

第二种方式：

/**
 * @auther: lawt
 * @date: 2018/12/1 17
 * @Description: 第二种启动方式
 */
@SpringBootApplication
public class MicroServicesSpringBootApplication1 {
public static void main(String[] args) {
//server.port=0 随机产生一个接口-随机向操作系统要一个可用的端口，
        new SpringApplicationBuilder(MicroServicesSpringBootApplication.class)
                .properties("server.port=0")
                .run(args);
    }
}

第三种启动方式：

/**
 * @auther: lawt
 * @date: 2018/12/1 17
 * @Description: 第三种启动方式
 */
@SpringBootApplication
public class MicroServicesSpringBootApplication2 {
public static void main(String[] args) {
        SpringApplication springApplication = new SpringApplication(MicroServicesSpringBootApplication2.class);
        Map<String, Object> properties = new HashMap<>();
        properties.put("server.port", 0);//不写端口，默认那是8080
        springApplication.setDefaultProperties(properties);
        springApplication.run(args);
    }
}

神奇的注解

@SpringBootApplication

咱们看看其源码：

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.context.TypeExcludeFilter;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.ComponentScan.Filter;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.core.annotation.AliasFor;
/**
 * Indicates a {@link Configuration configuration} class that declares one or more
 * {@link Bean @Bean} methods and also triggers {@link EnableAutoConfiguration
 * auto-configuration} and {@link ComponentScan component scanning}. This is a convenience
 * annotation that is equivalent to declaring {@code @Configuration},
 * {@code @EnableAutoConfiguration} and {@code @ComponentScan}.
 *
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @since 1.2.0
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
      @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
      @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
   @AliasFor(annotation = EnableAutoConfiguration.class)
    Class<?>[] exclude() default {};
   @AliasFor(annotation = EnableAutoConfiguration.class)
    String[] excludeName() default {}; 
   @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
    String[] scanBasePackages() default {};
   @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
    Class<?>[] scanBasePackageClasses() default {};
}

先看他上面的一个注解:

@ComponentScan

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Repeatable(ComponentScans.class)
public @interface ComponentScan {
    ......
 }

用于扫描，3.1版本来的，

再看它上面的另外一个注解：

@EnableAutoConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
   ...
}

激活自动装配 @Enable -> @Enable 开头的有：

• @EnableWebMvc
• @EnableTransactionManagement
• @EnableAspectJAutoProxy
• @EnableAsync

再看他上的另外一个注解：

@SpringBootConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {

}

等价于 @Configuration -> Configuration Class 注解